
module Logging

  # The +Logger+ class is the primary interface to the +Logging+ framework.
  # It provides the logging methods that will be called from user methods,
  # and it generates logging events that are sent to the appenders (the
  # appenders take care of sending the log events to the logging
  # destinations -- files, sockets, etc).
  #
  # +Logger+ instances are obtained from the +Repository+ and should
  # not be directly created by users.
  #
  # Example:
  #
  #    log = Logging.logger['my logger']
  #    log.add_appenders( Logging.appenders.stdout )   # append to STDOUT
  #    log.level = :info                               # log 'info' and above
  #
  #    log.info 'starting foo operation'
  #    ...
  #    log.info 'finishing foo operation'
  #    ...
  #    log.fatal 'unknown exception', exception
  #
  class Logger

    # Returns the root logger.
    def self.root
      ::Logging::Repository.instance[:root]
    end

    class << self
      alias_method :instantiate, :new  # `instantiate` becomes the "real" `new`
    end

    # Overrides the new method such that only one Logger will be created
    # for any given logger name.
    def self.new( *args )
      args.empty? ? super : self[args.shift]
    end

    # Returns a logger instance for the given name.
    def self.[]( name )
      repo = ::Logging::Repository.instance
      name = repo.to_key(name)
      logger = repo[name]
      return logger unless logger.nil?

      # Share the same mutex that's used by 'define_log_methods' because
      # it iterates over the hash of loggers, and adding a new key to a hash
      # while iterating over it produces an error.
      ::Logging::Logger.mutex.synchronize do
        logger = repo[name]
        return logger unless logger.nil? # thread-safe double checking

        logger = instantiate(name)
        repo[name] = logger
        repo.children(name).each { |child| child.__send__(:parent=, logger) }
        logger
      end
    end

    # This is where the actual logging methods are defined. Two methods
    # are created for each log level. The first is a query method used to
    # determine if that perticular logging level is enabled. The second is
    # the actual logging method that accepts a list of objects to be
    # logged or a block. If a block is given, then the object returned
    # from the block will be logged.
    #
    # Example
    #
    #    log = Logging::Logger['my logger']
    #    log.level = :warn
    #
    #    log.info?                               # => false
    #    log.warn?                               # => true
    #    log.warn 'this is your last warning'
    #    log.fatal 'I die!', exception
    #
    #    log.debug do
    #      # expensive method to construct log message
    #      msg
    #    end
    #
    def self.define_log_methods( logger )
      code = log_methods_for_level(logger.level)
      logger._meta_eval(code, __FILE__, __LINE__)
      logger
    end

    # This generator is used to define the log methods for the given `level`.
    # This code is evaluated in the context of a Logger instance.
    #
    # Returns log methods as a String
    def self.log_methods_for_level( level )
      code = []
      ::Logging::LEVELS.each do |name,num|
        code << <<-CODE
            undef :#{name}  if method_defined? :#{name}
            undef :#{name}? if method_defined? :#{name}?
        CODE

        if level > num
          code << <<-CODE
            def #{name}?( ) false end
            def #{name}( data = nil ) false end
          CODE
        else
          code << <<-CODE
            def #{name}?( ) true end
            def #{name}( data = nil )
              data = yield if block_given?
              log_event(::Logging::LogEvent.new(@name, #{num}, data, @caller_tracing))
              true
            end
          CODE
        end
      end
      code.join("\n")
    end

    @mutex = ReentrantMutex.new

    # Returns a global ReentrantMutex for use when creating Logger instances
    # and/or updating log levels.
    def self.mutex
      @mutex
    end

    attr_reader :name, :parent, :additive, :caller_tracing

    # call-seq:
    #    Logger.new( name )
    #    Logger[name]
    #
    # Returns the logger identified by _name_.
    #
    # When _name_ is a +String+ or a +Symbol+ it will be used "as is" to
    # retrieve the logger. When _name_ is a +Class+ the class name will be
    # used to retrieve the logger. When _name_ is an object the name of the
    # object's class will be used to retrieve the logger.
    #
    # Example:
    #
    #   obj = MyClass.new
    #
    #   log1 = Logger.new(obj)
    #   log2 = Logger.new(MyClass)
    #   log3 = Logger['MyClass']
    #
    #   log1.object_id == log2.object_id         # => true
    #   log2.object_id == log3.object_id         # => true
    #
    def initialize( name )
      case name
      when String
        raise(ArgumentError, "logger must have a name") if name.empty?
      else raise(ArgumentError, "logger name must be a String") end

      repo = ::Logging::Repository.instance
      _setup(name, :parent => repo.parent(name))
    end

    # call-seq:
    #    log <=> other
    #
    # Compares this logger by name to another logger. The normal return codes
    # for +String+ objects apply.
    #
    def <=>( other )
      case other
      when self; 0
      when ::Logging::RootLogger; 1
      when ::Logging::Logger; @name <=> other.name
      else raise ArgumentError, 'expecting a Logger instance' end
    end

    # call-seq:
    #    log << "message"
    #
    # Log the given message without any formatting and without performing any
    # level checks. The message is logged to all appenders. The message is
    # passed up the logger tree if this logger's additivity is +true+.
    #
    def <<( msg )
      @appenders.each {|a| a << msg}
      @parent << msg if @additive
    end
    alias_method :write, :<<

    # call-seq:
    #    add( severity, message = nil ) {block}
    #
    # Log a message if the given severity is high enough.  This is the generic
    # logging method.  Users will be more inclined to use #debug, #info, #warn,
    # #error, and #fatal.
    #
    # <b>Message format</b>: +message+ can be any object, but it has to be
    # converted to a String in order to log it. The Logging::format_as
    # method is used to determine how objects chould be converted to
    # strings. Generally, +inspect+ is used.
    #
    # A special case is an +Exception+ object, which will be printed in
    # detail, including message, class, and backtrace.
    #
    # If a _message_ is not given, then the return value from the block is
    # used as the message to log. This is useful when creating the actual
    # message is an expensive operation. This allows the logger to check the
    # severity against the configured level before actually constructing the
    # message.
    #
    # This method returns +true+ if the message was logged, and +false+ is
    # returned if the message was not logged.
    #
    def add( lvl, data = nil, progname = nil )
      lvl = Integer(lvl)
      return false if lvl < level

      if data.nil?
        if block_given?
          data = yield
        else
          data = progname
        end
      end

      log_event(::Logging::LogEvent.new(@name, lvl, data, @caller_tracing))
      true
    end

    # call-seq:
    #    additive = true
    #
    # Sets the additivity of the logger. Acceptable values are +true+,
    # 'true', +false+, 'false', or +nil+. In this case +nil+ does not
    # change the additivity
    #
    def additive=( val )
      @additive = case val
                  when true, 'true'; true
                  when false, 'false'; false
                  when nil; @additive
                  else raise ArgumentError, 'expecting a boolean' end
    end

    # call-seq:
    #    caller_tracing = true
    #
    # Sets the caller tracing of the logger. Acceptable values are +true+,
    # 'true', +false+, 'false', or +nil+. In this case +nil+ does not change
    # the tracing.
    #
    def caller_tracing=( val )
      @caller_tracing =
          case val
          when true, 'true'; true
          when false, 'false'; false
          when nil; @caller_tracing
          else raise ArgumentError, 'expecting a boolean' end
    end

    # call-seq:
    #    level    => integer
    #
    # Returns an integer which is the defined log level for this logger.
    #
    def level
      return @level unless @level.nil?
      @parent.level
    end

    # call-seq:
    #    level = :all
    #
    # Set the level for this logger. The level can be either a +String+, a
    # +Symbol+, or an +Integer+. An +ArgumentError+ is raised if this is not
    # the case.
    #
    # There are two special levels -- "all" and "off". The former will
    # enable log messages from this logger. The latter will disable all log
    # messages from this logger.
    #
    # Setting the logger level to +nil+ will cause the parent's logger level
    # to be used.
    #
    # Example:
    #
    #    log.level = :debug
    #    log.level = "INFO"
    #    log.level = 4
    #    log.level = 'off'
    #    log.level = :all
    #
    # These produce an +ArgumentError+
    #
    #    log.level = Object
    #    log.level = -1
    #    log.level = 1_000_000_000_000
    #
    def level=( level )
      @level =
        if level.nil? then level
        else
          lvl = case level
                when String, Symbol; ::Logging::level_num(level)
                when Integer; level
                else
                  raise ArgumentError,
                        "level must be a String, Symbol, or Integer"
                end
          if lvl.nil? or lvl < 0 or lvl > ::Logging::LEVELS.length
            raise ArgumentError, "unknown level was given '#{level}'"
          end
          lvl
        end

      define_log_methods(true)
      self.level
    end

    # Returns `true` if the logger has its own level defined.
    def has_own_level?
      !@level.nil?
    end

    # Returns the list of appenders.
    #
    def appenders
      @appenders.dup
    end

    # call-seq:
    #    appenders = app
    #
    # Clears the current list of appenders and replaces them with _app_,
    # where _app_ can be either a single appender or an array of appenders.
    #
    def appenders=( args )
      @appenders.clear
      add_appenders(*args) unless args.nil?
    end

    # call-seq:
    #    add_appenders( appenders )
    #
    # Add the given _appenders_ to the list of appenders, where _appenders_
    # can be either a single appender or an array of appenders.
    #
    def add_appenders( *args )
      args.flatten.each do |arg|
        o = arg.kind_of?(::Logging::Appender) ? arg : ::Logging::Appenders[arg.to_s]
        raise ArgumentError, "unknown appender #{arg.inspect}" if o.nil?
        @appenders << o unless @appenders.include?(o)
      end
      self
    end

    # call-seq:
    #    remove_appenders( appenders )
    #
    # Remove the given _appenders_ from the list of appenders. The appenders
    # to remove can be identified either by name using a +String+ or by
    # passing the appender instance. _appenders_ can be a single appender or
    # an array of appenders.
    #
    def remove_appenders( *args )
      args.flatten.each do |arg|
        @appenders.delete_if do |a|
          case arg
          when String; arg == a.name
          when ::Logging::Appender; arg.object_id == a.object_id
          else
            raise ArgumentError, "#{arg.inspect} is not a 'Logging::Appender'"
          end
        end
      end
      self
    end

    # call-seq:
    #    clear_appenders
    #
    # Remove all appenders from this logger.
    #
    def clear_appenders( ) @appenders.clear end

  protected

    # call-seq:
    #    parent = ParentLogger
    #
    # Set the parent logger for this logger. This method will be invoked by
    # the +Repository+ class when a parent or child is added to the
    # hierarchy.
    #
    def parent=( parent ) @parent = parent end

    # call-seq:
    #    log_event( event )
    #
    # Send the given _event_ to the appenders for logging, and pass the
    # _event_ up to the parent if additive mode is enabled. The log level has
    # already been checked before this method is called.
    #
    def log_event( event )
      @appenders.each {|a| a.append(event)}
      @parent.log_event(event) if @additive
    end

    # call-seq:
    #    define_log_methods( force = false )
    #
    # Define the logging methods for this logger based on the configured log
    # level. If the level is nil, then we will ask our parent for it's level
    # and define log levels accordingly. The force flag will skip this
    # check.
    #
    # Recursively call this method on all our children loggers.
    #
    def define_log_methods( force = false, code = nil )
      return if has_own_level? and !force

      ::Logging::Logger.mutex.synchronize do
        ::Logging::Logger.define_log_methods(self)
        ::Logging::Repository.instance.children(name).each do |child|
          child.define_log_methods
        end
      end
      self
    end

    # :stopdoc:
  public

    # call-seq:
    #    _meta_eval( code )
    #
    # Evaluates the given string of _code_ if the singleton class of this
    # Logger object.
    #
    def _meta_eval( code, file = nil, line = nil )
      meta = class << self; self end
      meta.class_eval code, file, line
    end

    # call-seq:
    #    _setup( name, opts = {} )
    #
    # Configures internal variables for the logger. This method can be used
    # to avoid storing the logger in the repository.
    #
    def _setup( name, opts = {} )
      @name      = name
      @parent    = opts.fetch(:parent, nil)
      @appenders = opts.fetch(:appenders, [])
      @additive  = opts.fetch(:additive, true)
      @level     = opts.fetch(:level, nil)

      @caller_tracing = opts.fetch(:caller_tracing, false)

      ::Logging::Logger.define_log_methods(self)
    end

    # call-seq:
    #    _dump_configuration( io = STDOUT, indent = 0 )
    #
    # An internal method that is used to dump this logger's configuration to
    # the given _io_ stream. The configuration includes the logger's name,
    # level, additivity, and caller_tracing settings. The configured appenders
    # are also printed to the _io_ stream.
    #
    def _dump_configuration( indent = 0 )
      str, spacer, base = '', '  ', 50
      indent_str = indent == 0 ? '' : ' ' * indent

      str << indent_str
      str << self.name.shrink(base - indent)
      if (str.length + spacer.length) < base
        str << spacer
        str << '.' * (base - str.length)
      end
      str = str.ljust(base)
      str << spacer

      level_str  = @level.nil? ? '' : '*'
      level_str << if level < ::Logging::LEVELS.length
        ::Logging.levelify(::Logging::LNAMES[level])
      else
        'off'
      end
      level_len = ::Logging::MAX_LEVEL_LENGTH + 1

      str << sprintf("%#{level_len}s" % level_str)
      str << spacer

      if self.respond_to?(:additive)
        str << (additive ? '+A' : '-A')
      else
        str << '  '
      end

      str << spacer
      str << (caller_tracing ? '+T' : '-T')
      str << "\n"

      @appenders.each do |appender|
        str << indent_str
        str << '- '
        str << appender.to_s
        str << "\n"
      end

      return str
    end
    # :startdoc:

  end
end
